1. Field of the Invention
The present invention relates to a porous metal based composite material which requires no pressuring mechanism during manufacture due to the spontaneous penetration of a metal which will become a matrix, or which can be manufactured under low pressure even if pressure is required, and the characteristic control thereof.
2. Description of the Related Art
Known methods of manufacturing porous materials include: (1) powder metallurgy techniques to sinter metal powders or short fibers; (2) directly adding a foam material to molten metal; (3) plating on foam plastic and removing the plastic; (4) forming a compound from a material having a small density, such as a foam material, and a metal; and (5) blowing gas into molten metal under zero gravity, for example.
However, in consideration of these methods, including the aspect of making a metal-based composite material porous, the powder metallurgy method (1) is uneconomical although the manufacture of Ti or Ti alloy stainless steel has been attempted. As an example of the method (2), Al alloy is foamed by using a hydride such as Ti and Zr. In this method, it is difficult to select a foam material for a steel material. It is also difficult to provide an even structure by foaming a composite material of metal and non-metal or the like. In the method (3), plastic is partially used as an organic material so that the application thereof is limited, which is troublesome. As an example of the method (4), Al alloy and Shirasu balloon-pumice are compounded. However, since hot molten metal has to be pressured and injected into an inorganic material having a small density, there are restrictions on a manufacturing facility. The method (5) presents difficulties in mass-production.
On the other hand, the present inventors discovered the application of a hard brazing material for a base which has little restriction on the types and shapes of the joining members which can be joined in various ways. By adding a fine particle material to the hard brazing material to lower thermal stress, an appropriate bonding strength is kept between different members. The joining strength around a joining interface is not lowered even by thermal stress during cooling after joining at high temperature, and also no cracks are formed at weak members by thermal stress during cooling, so that it was found that two or more different member scan be joined. In other words, the present inventors found that the above-noted properties can be obtained by an adhesive composition for bonding two or more different members. The adhesive composition consists of a hard brazing material and at least two types of fine particle materials having different wettabilities with respect to the hard brazing material. The present inventors thus applied for Japanese Patent Application No. 11-300184 as of Oct. 21, 1999. However, since this invention focuses on joining, there was not enough examination concerning the specific thickness of the adhesive composition or the application of the adhesive composition as a member itself at the time of the application.